Can an NSN number be used to cross-reference a fastener? 3

[KirbyWan]

Howdy all,

So if two different manufacturer's produce a fastener and list it under the same NSN number, would that be an acceptable justification to use it as an alternate? Are there any pitfalls to be aware of that would make them non-interchangeable?

Thanks,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[VEBill]

Overly short answer, no.

Our technique is to use the NSN to assist in finding a possible alternatives, but then obtain the actual OEM PN spec sheets to compare the details.

If the OEM PN spec sheets both point to the same Mil or Procurement spec, then you might be satisfied at that point.

If it's a critical application, then check the details.

Parts Lists typically use OEM PNs, not NSNs. Deviating from the approved PN may require Alternate PN Approval process.

Standby for others to chime in.

 

[WKTaylor]

KW... BE VERY-VERY-VERY careful specifying NSNs for parts.

First...

True part numbers clearly define the part [whatever it is] as intended... and rarely/never changes over decades. Also... these PNs [industry or corporate] are inevitably the qualified part for airworthiness certification.

Second...

NSNs are issued and controlled by DLA loggies... for procurement purposes. These folks rarely understand the potential extent and function/limitations/applications of the parts/materials they control.

I have seen NUMEROUS examples where parts, with variations, or 'equivalent to classification' were cross-listed to a single NSN... but variations were completely unacceptable.

In one case cadmium plated Inconel blind rivets were added to the NSN listing that included BARE rivets.. and were subsequently supplied across-the-board to USAF units. This was a lame attempt to eliminate NSNs for these distinctly different parts. Made perfect sense to 'them'... RIGHT???? WRONG... The bare rivets were to be installed in F100-100 engine titanium augmenter flaps. Cadmium plated blind rivets would metallic embrittle the titanium at the holes [silver and cadmium will embrittle titanium]. A single mechanic asked me 'why the newly received Inconel rivets on the shelf were all golden yellow colored?'. Thank God 'we' caught that aw-Sh*t in-time.

In another case, the qualified wheel-bearing 'set' [vendor's PNs] for F-15 landing gear were examined by DLA engineers... and 'determined' to be equivalent to MS stock bearings... without understanding WHY that specified PN was intended for the specified application. When an NLG wheel froze-up and the tire and 1/4 of the wheel were scraped-off, We discovered miss-matched MS bearings [inner/outer races made by different vendors] that had failed, during the mishap tear-down inspection. When I informed the F-15 Landing gear engineer about this he went ballistic: these inferior substitutes had been issued for several months for the NLG & MLG wheels... and there was an emergency action [STCTO] issued to get these bearings out of landing gear and get the qualified bearings installed. BUT... the 'problem' was really a LOT worse than JUST the F-15!!!... NOT ONLY had DLA substituted MS bearings for the F-15... It had done so 'quietly' for MOST of the other aircraft in the inventory. Huge 'cost savings' for DLA... but a nightmare for the landing gear folks at OO-ALC.

I have also seen many 'good intended substitutions' within single NSNs for certain process chemicals: finish materials, epoxies, tapes, etc. same situation. You can get what you get... from the lowest bidder. These substitutes can bring maintenance operations to a stand-still if they are inappropriate.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[KirbyWan]

I knew about cadmium embrittlement of titanium, I didn't know silver also caused this effect. Thanks for your detailed response. So I can use NSN to find other possibilities, and then dig into them to make sure they are equivalent. I often get my purchaser saying that when she ordered a fastener the vendor offers an alternate part number. If I can find it and compare it, I feel okay about it. Occasionally I get a part number that has no information about it at all. I'm guessing the vendor is using a stock line number that has nothing to do with the part.

Thanks all

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[VEBill]

There's also the concept of Approved Vendors / Suppliers.

The OEM PN should lead back to a supplier and ultimately the specific manufacturer that have been explicitly Approved by QA.

Suddenly switching to an Alternate PN, especially from a different supplier, bypasses all that. QA would be justifiably upset.

Note that this consideration remains a legitimate concern even if the Alternate PN is precisely identical to the original PN.

We've spent days trying to figure out the exact PNs that were in stock, so that we could ensure that the Parts List matched what was actually available. In spite of our best efforts, the available PNs drifted and we then had further effort to chase those changes. As our applications were non-critical, our PLs ended up including all sorts of alternates. And we still had some Deviations.

Crikey. 2018 and many processes are still far from optimized.

 

[Gary_321]

If by NSN, you mean NATO Stock Number (called National Stock Number in the US), I might be able to help. I used to codify NSNs.

You have to know what the codes mean. The most common are...

A 3-2 reference is the prime reference. It is the manufacturer's part number who actually makes the part and the part number is fully definitive.

A 5-2 reference is a secondary reference. It is a supplier's part number and is fully definitive.

A 6-9 is purely informative and is only to be used for guidance. In the rivet example above, a 6-9 should have been used for the coated rivets on the bare rivet's NSN and vice versa. This doesn't mean that they are interchangeable, it means that you will be steered towards all the NSNs for that SIZE of rivet.

What is the NSN that you are looking at?

 

[KirbyWan]

Gary_321,

Thanks for your response. Let me go through the parts and my searches to see if I could be more confident in my fastener selections.

I was looking for an MA13601-048-3 and MA13601-048-2 nutplate. We could get the -3 with no problem, but the -2 was elusive. My purchaser said a vendor was offering an S987DC4-2. So I was using an NSN search to see if I could confirm what the vendor was proposing as an alternate. Aerobasegroup and part target came up with 5310-01-333-2853 as an NSN and following their link one other part on the same NSN which was C068-048-2. (WB parts came up with 5310-01-442-6809 which was listed as a cancelled NSN on the parttarget website)

The same search for MA13601-048-3 found more results associated with NSN 5310-00-809-7437 including HS4482-048-3, M13601-048-3, and RM12LHA3006M3-048. It also listed cancelled NSN 5310-01-467-0572.

Going in the other direction I searched for S987DC-4-3 and came up with NSN 5310-01-126-4750. C068-048-3, RFM22A3-4, RM52LHA3006M3-048.

We purchased the S987DC4-2 and I did a visual comparison with the MA13601-048-3 that we could purchase and they looked identical in style and coatings, different in the height of the nut, I expect so they could use a common length fastener. There's some overlap in part number formats, particularly the C068-048-X part numbers.

I'd love to learn more about the NSN formats. Where in the NSN number can I find the 3-2, 5-2 and 6-9 you're talking about?

Thanks for your help.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[VEBill]

Look into: Reference Number Variation Code (RNVC) and Reference Number Category Code (RNCC).

Perhaps Google: NSN RNCC/RNVC

It's a big topic. Good luck.

Hopefully Gary will return as he probably knows more than I on this topic.

PS: You probably still have to have an Engineer verify the OEM spec sheets if it's a critical part. And there may still be an Alternate Part approval process to go through. But YMMV.

 

[Gary_321]

Search results for MA13601-048-3

The first record (5310-00-809-7437) is the only one with MA13601-048-3 as a reference. The other records are close matches, not "hits".

Opening 5310-00-809-7437 (link), we can see that...

1. MA13601-048-3 is a 5-9 reference. The 9 is the most significant part of the code. It means that the reference is for information ONLY. The 5 means that it is a "secondary" reference.
2. The primary reference is M13601-048-3. It is a 3-2 reference. The 2 means that the part number (M13601-048-3) FULLY defines the item to the company with the Cage Code 80539. The 3 means that 80539 are the holders of the design rights for the item.
3. If you ask the SPS Technologies Parts Department to supply a M13601-048-3, you should not need to give them any more information than that. They should supply you with the part defined in the NSN.

 

[Gary_321]

Search results for MA13601-048-2

The first record (5310-01-333-2853) is the only one with MA13601-048-2 as a reference. The other records are close matches, not "hits".

Opening 5310-01-333-2853 (link), we can see that...

1. The primary reference is MA13601-048-2. It is a 3-2 reference. The 2 means that the part number (MA13601-048-2) FULLY defines the item to the company with the Cage Code 80539. The 3 means that 80539 are the holders of the design rights for the item.
2. If you ask the SPS Technologies Parts Department to supply a MA13601-048-2, you should not need to give them any more information than that. They should supply you with the part defined in the NSN.


n.b. Having seen the other NSN record, I suspect this NSN record is not 100% accurate. If I were still working for the UK MOD, I would be investigating this NSN. I suspect that the correct SPS part number is M13601-048-2. A quick phone call to SPS would confirm.

Also, there is a second primary reference on this record. This is not usually correct, as there will only be one design rights holder, unless there has been a company takeover, and both company names are trading.

I suspect the part is made by SPS and Lockheed Martin fit the part to one of their systems, and have given the part one of their part numbers. If this is the case, the Lockheed Martin part number should be a 5-2 reference.

The record is correct if Lockheed Martin have taken over control of SPS (or vice versa) and both Lockheed Martin AND SPS are trading.

If Lockheed Martin have taken over SPS and SPS has stopped trading, the SPS reference should be a 6-9. This would allow you to find the SPS part number, but would know that you couldn't buy the part from SPS, but could buy it from Lockheed Martin.

 

[KirbyWan]

The part as listed on the drawing and parts list for DC-10 (KC-10) nose cowl NSL6052 is MA13601-048-2 and -3. Can I go from a secondary reference of MA13601-XXX-Y to a primary reference for M13601-XXX-Y? That seems obvious, but without diving deep into the significance of the classification of NSN numbers I'd rather ask the question then be wrong.

I will dig into the details of NSN numbers. Thanks for your help Gary, VE1BLL and Wil. These nut plates are holding on the access covers on the outer barrel. Not what I would call critical, I think I'm overthinking this, but I'd rather learn from an issue in a non-critical area so I have the knowledge when I need it for a critical area.

Best Regards,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[Gary_321]

If you are buying the part, it is irrelevant whether it is a primary or a secondary reference. It is more important to know whether the part number is fully defined, or if it is not, what additional information you need to give.

If you order an NSN, you should be issued with the part that NSN describes.

A primary reference is usually the reference from the original supplier of the PART.
A secondary reference is usually the reference from the supplier of the SYSTEM.

Each NSN is FULLY defined, but not all manufacturer's part numbers are. Imagine the following...
Hypothetical NSN 1234-12-123-1234
a) Bosch design and manufacture fuel injectors. They hold the design rights for that fuel injector. The part number would be the primary reference and is fully defined by Bosch (3-2).
b) BMW supply Bosch fuel injectors with a BMW part number ON THE BOX. The BMW part number would be the secondary reference and is fully defined (5-2).
c) The same fuel injector is also fitted on a Land Rover. The Land Rover part number would be another fully defined secondary reference (5-2).
d-1) Perkins supply the same fuel injector, but their part number is not fully defined as you need to tell them the flow rate. Their part number would be a 5-1 reference.
d-2) The Perkins part number would appear on multiple NSNs. Each NSN would be for a similar fuel injector, but each would have a different flow rate.


Looking at your nut plates, if I had been codifying the NSNs, I would have been tempted to add M13601-048 as a 5-1 and MA13601-048 as a 6-9 reference to each record.
There is an "as defined by" field (CXCY, if I recall correctly, but it's been over 15 years) that should be completed if a 5-1 is used.